An Auxiliary power unit (APU) is provided in an aircraft to provide power to aircraft systems to either supplement or substitute power generated by the main engines. An APU is typically a small gas turbine engine that is mounted within the aircraft fuselage and which draws air through inlets defined within the outer skin of the aircraft. The compressor section includes a compressor wheel that includes contoured blades. The contoured blades are subject to flow forces and rotational forces that may generate a resonance frequency in the contoured blades.